1. Field of the Invention
The present invention relates to a method of determining the characteristics of a signal and an apparatus using the method, and more particularly, to a method of determining the characteristics of a RF signal obtained from an optical disc and an apparatus using the same.
2. Description of Related Art
A beam reflected from an optical disc is converted into an electric signal to generate binary data which is recorded in the optical disc by a specified signal processing technique. A signal obtained by converting the beam reflected from the optical disc into the electric signal is called a RF (Radio Frequency) signal. Even though binary data is recorded in the optical disc, the RF signal obtained from the optical disc has analog signal properties due to the characteristics of the optical disc and optical characteristics. The RF signal is binarized to obtain the binary data.
Typically, a variety of indexes that indicate the characteristics of the RF signal obtained from the optical disc exist. Such indexes include, for example, an asymmetry of RF signal and a modulation ratio of the same. The RF signal includes a signal having various periods depending on the modulation of data and which code is used. For example, in a case where the RF signal is modulated using a (2,10) code, a 3T signal that is 3 times the basic feet period is a signal having the shortest period and an 11T signal is a signal having the longest period. The asymmetry is a scale indicating how far the center of a signal having a specified period shorter than the longest period is away from the center of a signal having the longest period. The modulation ratio is a scale indicating how small the size of the signal having a specified period shorter than the longest period is compared to the size of signal having the longest period. FIG. 1 is a graph illustrating an eye-pattern signal in order to describe the asymmetry and modulation ratio. The eye-pattern eye is obtained by simultaneously displaying signals having a variety of periods obtained from the optical disc on an oscilloscope.
Referring to FIG. 1, 11TTOP and 11TBTM indicate the maximum value and the minimum value, respectively, of the 11T signal, which is a signal having the longest period, in a case where a signal is modulated using a (2,10) code. 3TTOP and 3TBTM indicate the maximum value and the minimum value, respectively, of the 3T signal, which is a signal having the shortest period. The asymmetry and modulation ratio of the RF signal are calculated using 11TTOP, 11TBTM, 3TTOP, and 3TBTM. The asymmetry and modulation ratio are disclosed in detail in U.S. Pat. No. 5,490,127.
The foregoing asymmetry and modulation ratio are required to have a value within a specified range so that a data recording and/or reproducing device in which the optical disc is loaded can reproduce the data recorded in the optical disc without error. Therefore, it is essential to exactly measure scale indicating characteristics of the RF signal such as asymmetry and modulation ratio, etc.
However, an increase in recording density of the optical disc and/or deterioration of recording quality thereof result in deteriorating quality of the RF signal obtained from the optical disc. Accordingly, it is difficult to exactly determine a scale that indicates the characteristics of the RF signal such as asymmetry and modulation ratio, etc.